On Sat, Apr 21, 2018 at 12:59:23PM +0200, Paul Kocialkowski wrote: > Hi, > > Le vendredi 20 avril 2018 à 09:25 -0500, Bin Liu a écrit : > > On Thu, Mar 29, 2018 at 01:57:24PM +0200, Paul Kocialkowski wrote: > > > Hi, > > > > > > On Thu, 2018-03-29 at 11:23 +0200, Maxime Ripard wrote: > > > > On Wed, Mar 28, 2018 at 11:52:13PM +0200, Paul Kocialkowski wrote: > > > > > This allows dual-role ports to be reported as having gadget mode > > > > > by > > > > > the > > > > > musb_has_gadget helper. This is required to enable MUSB at all > > > > > with > > > > > MUSB > > > > > glue layers that set the port mode to MUSB_PORT_MODE_DUAL_ROLE > > > > > at > > > > > init. > > > > > > > > > > Most notably, this allows calling musb_start when needed in the > > > > > virtual > > > > > MUSB root HUB, regardless of whether the current mode should be > > > > > gadget > > > > > or host. > > > > > > > > > > This fixes USB OTG on Allwinner devices that I could test it > > > > > with, > > > > > mainly A20 devices. > > > > > > > > > > Signed-off-by: Paul Kocialkowski > > > > > > > > Surely there's more to it than that. The gadget mode of A20 boards > > > > have been working in the past, including when compiling with mUSB > > > > setup as dual role. > > > > > > > > Is this a regression since a particular commit? Or is there > > > > another, > > > > deeper issue overlooked in the commit log? > > > > > > The root of the issue here is that musb_start is not called at any > > > point > > > without this patch. My understanding of the flow is the following: > > > when > > > the PHY detects that there was a VBUS/ID change, it will notify its > > > listeners (mainly the musb sunxi glue layer). This will then > > > schedule > > > the driver's work (sunxi_musb_work), which does nothing since the > > > SUNXI_MUSB_FL_ENABLED bit was never set. This bit is only set after > > > calling sunxi_musb_enable, which is called from > > > musb_platform_enable, > > > that originates from musb_start. > > > > > > Currently I see two places where musb_start is called: > > > * musb_virthub > > > * musb_gadget > > > > > > In the latter case, it is in turn called from udc_start, which > > > should > > > probably (correct me if I'm wrong) happen later in the call chain > > > than > > > ID/VBUS change notification time. > > > > I don't think it is correct that udc_start() is triggered by ID/VBUS > > events, but I don't have an Allwinner platform to verify the callflow. > > Yes you're right, I didn't make myself very clear here. I didn't > investigate the udc_start call path much since it was apparently not the > culprit. > > > Have you tried to load with a gadget driver? When a gadget function is > > bound to UDC, udc_start() is triggered, which in turn calls > > musb_start(). > > It does work under that scenario, although my used case here is using > musb with DUAL_ROLE but no gadget driver loaded. That it, I want the > musb_start call to originate from the virtual hub, not from the gadget > side. > > > > In the former case, musb_start is called in the root controller hub > > > control, when setting the USB_PORT_FEAT_POWER feature. This looks > > > perfectly legit and IMO this is where it should be initially calling > > > musb_start in the dual role case. The kernel is indeed setting the > > > > No actually. A dual-role port should be in b_idle state by default, so > > logically all actions should go to the gadget path until the port > > switches to host mode. > > It makes sense that the port should be in b_idle state by default, but > here it fails to switch to host mode when the ID pin detects that it > should. Or does b_idle state entail that a gadget must be loaded (per > the USB spec), and thus nothing should (ever) happen until that happens? > > I find it really odd to need a gadget device to trigger host mode. > This patch does fix the issue, but I am puzzled as to why it is needed > in the first place. The comment above it mentions that "In OTG mode we > have to wait until we loaded a gadget. We don't really need a gadget if > we operate as a host but we should not start a session as a device > without a gadget or else we explode.", which is apparently compatible > with my use case: a gadget is not really needed and I'm not trying to > start a session as a device without a gadget loaded. > > What do you think? Okay, this came down to an argument that whether we should require loading a gadget driver on a dual-role port to work in host mode, which is currently required on musb since a long long time ago. I understand the requirement is kinda unnecessary, but since it already exists on musb stack for a long time, I don't plan to change it. Because I cannot think of a use case in real products that doesn't automatically load a gadget function on the dual-role port. If you can explain a use case in real world (not a engineering lab) that the gadget driver will not be loaded at linux booting up, but later based on user's input, I will reconsider my decision. To remove this requirement from musb stack, the work is more than this patch. Regards, -Bin.